1. Field of the Invention
The present invention relates to an electromagnetic wave shielding sheet to shield electromagnetic waves produced from displays such as cathode-ray tubes (CRT) or plasma display panels (PDP.) In particular, the present invention relates to a protective film that causes no discoloration of an electromagnetic wave shielding sheet even after long-term storage at high temperature and high humidity, a method for producing the protective film, and an electromagnetic wave shielding sheet with the protective film.
2. Description of the Related Art
With the sophistication of function and the increasing use of electrical and electronic devices in recent years, electromagnetic interference (ERI) has increased and displays such as cathode-ray tubes and plasma display panels produce electromagnetic waves. To shield the electromagnetic waves, electromagnetic wave shielding sheets to be disposed on the front face of a display is known. Such electromagnetic wave shielding sheets are demanded to have optical transparency as well as electromagnetic wave shielding capability. Accordingly, electromagnetic wave shielding sheets provided with optical transparency by using a transparent substrate such as a resin film or a glass plate as a substrate and forming thereon a conductive mesh layer of metal such as copper are known.
Sometimes optical filters such as an antireflection filter and a near-infrared filter are mounted on the front face of a display so that in many cases an electromagnetic wave shielding sheet is laminated to the optical filters through an adhesive layer and disposed on the front surface of a display as a composite filter. For example, Japanese Patent Application Laid-Open (JP-A) No. 11-126024 discloses a front surface plate of a display panel in which an antireflection film is attached to a filter film for shielding electromagnetic waves through a tacky adhesive layer.
Sometimes a protective film is temporarily laminated to the electromagnetic wave shielding sheet to protect the mesh layer until the electromagnetic wave shielding sheet is disposed on the front face of a display or laminated to other optical filters, etc. JP-A No. 2003-188576 discloses an electromagnetic wave shield sheet comprising a protective film to protect a transparent base film or an electromagnetic wave shielding layer in handling or production of the products.